<?php


namespace app\common\service\encryption;


class AlphaID
{
    /**
     * Translates a number to a short alhanumeric version
     *
     * Translated any number up to 9007199254740992
     * to a shorter version in letters e.g.:
     * 9007199254740989 --> PpQXn7COf
     *
     * specifiying the second argument true, it will
     * translate back e.g.:
     * PpQXn7COf --> 9007199254740989
     *
     * this function is based on any2dec && dec2any by
     * fragmer[at]mail[dot]ru
     * see: http://nl3.php.net/manual/en/function.base-convert.php#52450
     *
     * If you want the alphaID to be at least 3 letter long, use the
     * $pad_up = 3 argument
     *
     * In most cases this is better than totally random ID generators
     * because this can easily avoid duplicate ID's.
     * For example if you correlate the alpha ID to an auto incrementing ID
     * in your database, you're done.
     *
     * The reverse is done because it makes it slightly more cryptic,
     * but it also makes it easier to spread lots of IDs in different
     * directories on your filesystem. Example:
     * $part1 = substr($alpha_id,0,1);
     * $part2 = substr($alpha_id,1,1);
     * $part3 = substr($alpha_id,2,strlen($alpha_id));
     * $destindir = "/".$part1."/".$part2."/".$part3;
     * // by reversing, directories are more evenly spread out. The
     * // first 26 directories already occupy 26 main levels
     *
     * more info on limitation:
     * - http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/165372
     *
     * if you really need this for bigger numbers you probably have to look
     * at things like: http://theserverpages.com/php/manual/en/ref.bc.php
     * or: http://theserverpages.com/php/manual/en/ref.gmp.php
     * but I haven't really dugg into this. If you have more info on those
     * matters feel free to leave a comment.
     *
     * @author  Kevin van Zonneveld <kevin@vanzonneveld.net>
     * @author  Simon Franz
     * @author  Deadfish
     * @copyright 2008 Kevin van Zonneveld (http://kevin.vanzonneveld.net)
     * @license   http://www.opensource.org/licenses/bsd-license.php New BSD Licence
     * @version   SVN: Release: $Id: alphaID.inc.php 344 2009-06-10 17:43:59Z kevin $
     * @link    http://kevin.vanzonneveld.net/
     *
     * @param mixed   $in    String or long input to translate                                     TODO 需要加密的
     * @param boolean $to_num  Reverses translation when true                                      TODO false加密 true解密
     * @param mixed   $pad_up  Number or boolean padds the result up to a specified length         TODO 指定生成字母ID的长度为6
     * @param string  $passKey Supplying a password makes it harder to calculate the original ID   TODO 加盐
     *
     * @return mixed string or long
     */
    public function alphaID($in, $to_num = false, $pad_up = false, $passKey = null)
    {
        $index = "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        if ($passKey !== null) {
            // Although this function's purpose is to just make the
            // ID short - and not so much secure,
            // with this patch by Simon Franz (http://blog.snaky.org/)
            // you can optionally supply a password to make it harder
            // to calculate the corresponding numeric ID

            for ($n = 0; $n<strlen($index); $n++) {
                $i[] = substr( $index,$n ,1);
            }

            $passhash = hash('sha256',$passKey);
            $passhash = (strlen($passhash) < strlen($index))
                ? hash('sha512',$passKey)
                : $passhash;

            for ($n=0; $n < strlen($index); $n++) {
                $p[] =  substr($passhash, $n ,1);
            }

            array_multisort($p,  SORT_DESC, $i);
            $index = implode($i);
        }

        $base  = strlen($index);

        if ($to_num) {
            // Digital number  <<--  alphabet letter code
            $in  = strrev($in);
            $out = 0;
            $len = strlen($in) - 1;
            for ($t = 0; $t <= $len; $t++) {
                $bcpow = bcpow($base, $len - $t);
                $out   = $out + strpos($index, substr($in, $t, 1)) * $bcpow;
            }

            if (is_numeric($pad_up)) {
                $pad_up--;
                if ($pad_up > 0) {
                    $out -= pow($base, $pad_up);
                }
            }
            $out = sprintf('%F', $out);
            $out = substr($out, 0, strpos($out, '.'));
        } else {
            // Digital number  -->>  alphabet letter code
            if (is_numeric($pad_up)) {
                $pad_up--;
                if ($pad_up > 0) {
                    $in += pow($base, $pad_up);
                }
            }

            $out = "";
            for ($t = floor(log($in, $base)); $t >= 0; $t--) {
                $bcp = bcpow($base, $t);
                $a   = floor($in / $bcp) % $base;
                $out = $out . substr($index, $a, 1);
                $in  = $in - ($a * $bcp);
            }
            $out = strrev($out); // reverse
        }

        return $out;
    }
}